High-k gate dielectrics prepared by liquid phase anodic oxidation

ABSTRACT

A method of high-k gate dielectrics prepared by liquid phase anodic oxidation, which first produces a metallic film on the surface of a clean silicon substrate, next to oxidize said metallic film to form a metallic oxide as a gate oxidizing layer by liquid phase anodic oxidation, then to promote quality of said gate oxidizing layer by processing a step of thermal annealing. With this oxidation, a gate dielectric layer of high quality, high-k and ultrathin equivalent oxide thickness (EOT) can be produced, which can be integrated to complementary metal oxide semiconductor (CMOS) process directly.

BACKGROUND OF THE INVENTION

[0001] The present invention relates to a method of high-k gate dielectrics prepared by liquid phase anodic oxidation, and more particularly to a method of using liquid phase anodic oxidation to produce a gate dielectric layer of high quality, high-k (k; dielectric constant) and ultrathin equivalent oxide thickness (EOT), which can be integrated to complementary metal oxide semiconductor (CMOS) process directly.

[0002] The present technology of complementary metal oxide semiconductor process has reached to the times of deep sub-micron device. The more advanced nanotechnology process (<100 nm) also researchs and develops rapidly close to the period of manufacturing. Following the continuous advanced technique of process, the gate-oxidizing layer of the transistor is getting thinner. Though the advantages of prior silicon dioxide can't be replaced, the leakage current in the accumulation region performs a trend of exponential growth with the decreasing of thickness. Therefore, high-k materials need to be researched and developed as gate oxidizing layers. A high-k gate oxidizing layer has lower leakage current compared with same equivalent oxide thickness and very possible replaces silicon dioxide to be a gate oxidizing layer inside the transistor in the next generation.

[0003] The general prior arts to produce a thin high-k metal oxidizing layer chiefly include thermal oxidation, molecular beam epitaxy (MBE), chemical vapor deposition (CVD) and atomic layer deposition (ALD). Therein thermal oxidation has to deposit a layer of metal or a compound containing the metal on the substrate and then produces the metal oxidizing layer by thermal oxidation. Though the traditional method is easy and convenient, it must be processed under high tempature. The metal oxidizing layer can be produced on the substrate directly by MBE, CVD or ALD, instead of expensive installations used to form a high vacuum environment under high tempature.

[0004] As regard to the technology of 0.13 μm (micron) process that being used in the manufacturing, thickness of a gate oxidizing layer of a transistor is about to 24 Å. When the thickness of a gate oxidizing layer is smaller than 30 Å, isolation of a gate oxidizing layer will get much influenced by the direct tunneling effect, results in the increment of leakage current of a oxidizing layer to cause power dissipation of the transistor in the closed situation and the possibility of wrong switched circuit. When devices are getting minimizing, current driving ability of the transistors also get decreasing. From the current formula of the metal oxide semiconductor field effect transistor (MOSFET),

I _(d)=1/2·C _(ox) ·W/L(V _(gs) −V _(t))²

[0005] Therein, I_(d) means current,

[0006] μL means mobility,

[0007] C_(ox) means capacity of oxidizing

[0008] W means channel width,

[0009] L means channel length,

[0010] V_(gs) means voltage of gate corresponds to source,

[0011] V_(t) means threshold voltage.

[0012] We know that if we want to increase the current of the transistor, we must first increase C_(ox) so as to keep a stable current driving ability while the characterized size of devices are getting minimizing.

[0013] To solve foregoing problems, to increase physical thickness and value of dielectric constant so as to decrease leakage current of an oxidizing layer and to increase C_(ox). Therefore, using high-k materials to replace silicon dioxide as gate oxidizing layers is a necessary trend. The high-k gate oxidizing layers also calls high-k gate dielectrics. It is therefore tried by the inventor to develop a method of high-k gate dielectrics prepared by liquid phase anodic oxidation, which first produces a metallic film on the surface of a clean silicon substrate, next oxidizes said metallic film to forma metallic oxide as a gate oxidizing layer by liquid phase anodic oxidation, then promotes quality of said gate oxidizing layer by processing a step of thermal annealing. With this oxidation, a gate dielectric layer of high quality, high-k and ultrathin equivalent oxide thickness can be produced, which can be integrated to complementary metal oxide semiconductor process directly.

SUMMARY OF THE INVENTION

[0014] A primary object of the present invention is to provide a method of high-k gate dielectrics prepared by liquid phase anodic oxidation, which first produces a metallic film on the surface of a clean silicon substrate, next oxidizes said metallic film to form a metallic oxide as a gate oxidizing layer by liquid phase anodic oxidation, then promotes quality of said gate oxidizing layer by processing a step of thermal annealing, with this oxidation, a gate dielectric layer of high quality, high-k and ultrathin equivalent oxide thickness can be produced, which can be integrated to complementary metal oxide semiconductor process directly.

[0015] Another object of the present invention is to provide a method of producing a metal oxide semiconductor field effect transistor that contains high-k gate dielectrics, which first produces a p-well and a n-well on a silicon substrate and fills an oxide for isolation. Then to produce a metallic film on the surface of said clean silicon substrate and to oxidize said metallic film to form a metallic oxide as a gate-oxidizing layer by liquid phase anodic oxidation. Next promoting quality of said gate oxidizing layer by processing a step of thermal annealing so as to form a gate layer on the gate metal oxidizing layer. To definite the gate region and to form the gate, drain and source of the transistor by ion implantation, then depositing an oxide-isolating layer on the gate layer. After etching the window of the gate, drain and source, deposits a contact wire, and decreases concentration of junction traps by using thermal annealing so as to produce a metal oxide semiconductor field effect transistor that contains high-k gate dielectrics.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The structure and the technical means adopted by the present invention to achieve the above and other objects can be best understood by referring to the following detailed description of the preferred embodiments and the accompanying drawings, wherein

[0017]FIG. 1 is a diagram that shows the producing process of high-k gate dielectrics that can be integrated to complementary metal oxide semiconductor process (take Al₂O₃ for the example).

[0018]FIG. 2 is a diagram that shows the composition of liquid phase anodic oxidation.

[0019]FIG. 3 is a diagram that shows a change of gate voltage corresponds to time, while injects a constant current of −1 mA/cm² to gate of Al₂O₃ MOS device.

[0020]FIG. 4 is a diagram that shows current-voltage (I-V) characters of Al₂O₃ whose EOT is 23 Å.

[0021]FIG. 5 is a diagram that shows a high-k Al₂O₃ dielectric layer whose k is 9.7 by calculating from values of EOT corresponds to optical thickness.

[0022]FIG. 6 is a diagram that shows the comparison of leakage current of Al₂O₃ and SiO₂ under different equivalent oxide thickness.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0023] Embodiment 1

[0024] Please refer to FIGS. 1(a)˜(e), are diagrams that shows the producing process of high-k gate dielectrics that can be integrated to complementary metal oxide semiconductor process (take Al₂O₃ for the example). As shown, to oxidize a metal to form a metallic oxide by liquid phase anodic oxidation so as to produce a high-k gate dielectric. The first step of the process is producing a p-well 2 and a n-well 3 on a P-silicon substrate 1 and filling an oxide 4 for isolation (as shown in FIG. 1(a)). Then deposits a layer of ultrathin metallic aluminum film 5 on a clean P-silicon substrate 1 by evaporation or sputtering (as shown in FIG. 1(b)). Next oxidizing the metal to form a metal oxidizing layer by liquid phase anodic oxidation (see FIG. 1(c), anode 6 is a P-silicon substrate 1, cathode 7 is a platinum sheet, electrolyte 8 is DI water or other organic, inorganic electrolyte). And to promote quality of the oxidizing layer by annealing (not shown) to form a gate aluminum oxide 9, finally to produce a poly-silicon gate 91 to work out a high-k gate dielectric (as shown in FIGS. 1(a)˜(e))

[0025] Embodiment 2

[0026] To take an example of preparing metal oxide semiondutor diode (MOS diode) by direct current anodic oxidation in DI water 81. As described in the foregoing preparing steps, First to deposit a 15 Å pure aluminum film (99.9999%) on a clean silicon substrate by evaporation. Then processes direct current anodic oxidation in DI water 81 which using value of electric field is 7.143 V/cm and oxidizing time is 6.5 minutes, as shown in FIG. 2. Thereafter to proceed annealing under high tempature by using furnace under nitrogen gas, and the annealing tempature is 650° C., the annealing time is 60 seconds, and comes out the preparation of the oxidizing layer whose gate is an aluminum metal that produced by evaporation (3000 Å). After that, to definite the gate area (2.25·10⁻⁴ cm²) by photolithography and finally to evaporate aluminum metal again as a back contact of a chip to finish fabrication of whole single device. EOT of the aluminum oxide film is 23 Å.

[0027] As for fabricating a metal oxide semiconductor field effect transistor, to produce the gate, source and drain of the transistor by ion implantation after finishing the definition of gate area. And to deposit a contact wire on the gate, source and drain so as to form a metal oxide semiconductor field effect transistor.

[0028] In the above-mentioned embodiments, of course, the metallic film produced on the surface of said silicon substrate must isolate the electrode to make only the back of the silicon substrate can be contacted with the electrode so as to form a well-proportioned oxidizing electric field.

[0029] Analysis of the results in the above-mentioned embodiments is as follows,

[0030] To research the importance of annealing under high tempature toward the character of the device, we inject a constant current of −1 mA/cm² into the end of the gate of the MOS device to observe the change of gate voltage.

[0031] The result is shown in FIG. 3, the oxidizing layer contains a lot of electron and hole traps before the device processes annealing under high tempature. When the electrons and holes are trapped while passing the oxidizing layer, result in the large libration of gate voltage. But there are much improvement of the libration change of gate voltage after annealing under high tempature can be seen. From those we can understand the importance of annealing under high tempature that contributed to improvement of quality of dielectrics after anodic oxidation.

[0032] Current-voltage (I-V) character of the device has shown in FIG. 4, leakage current of aluminum oxide was lower 100˜1000 times than that of silicon dioxide which can be got in the accumulation region, while whole full current can be got in the depletion region and inversion region. The whole full current will enable channel mobility to produce a mild decay.

[0033]FIG. 5 is a diagram that draws from the value of optical thickness measured by ellipsometer and EOTs measured by C-V. From the following related formula,

ε _(ox) /EOT=ε _(Al) ₂ _(O) ₃ /T _(Al) ₂ _(O) ₃

ΔEOT/ΔT _(Al) ₂ _(O) ₃ =ε_(ox)/ε_(Al) ₂ _(O) ₃

[0034] Therein, ε_(ox) means dielectric onstant of oxidizing layer,

[0035] EOT means equivalent oxide thickness,

[0036] ε_(Al) ₂ _(O) ₃ means dielectric onstant of aluminum oxide,

[0037] T_(Al) ₂ _(O) ₃ means optical thickness of aluminum oxide.

[0038] We can get a high-k Al₂O₃ dielectric whose k (ε_(Al) ₂ _(O) ₃ ) is 9.7.

[0039]FIG. 6 is a diagram that shows the comparison of leakage current of Al₂O₃ and SiO₂ under different equivalent oxide thickness. We know that the process is a stable process which can be reproduced, and get lower leakage current than SiO₂'s by all different values of EOT.

[0040] Compared with above-mentioned better embodiments and get following features of the invention,

[0041] 1. A film of the metal oxidizing layer that produced by liquid phase anodic oxidation can be a gate dielectric of a MOSFET. This method can get excellent oxidation control toward metallic film under room tempature so that metal oxidizing layer of high quality and high-k can be produced. Furthermore, EOT of the metal oxidizing layer can decrease to 14 Å and still remain better electric characters. In the furture advanced process above 0.13 micron technology, EOT would lower than 0.20 Å. Accordingly, the invention that can be integrated to the most advanced process will play an important role in the fabrication of the gate oxidizing layer.

[0042] 2. The invention takes cheap and effective liquid phase anodic oxidation, which first deposits a layer of metal on a substrate and effectually oxidizes the deposited metal to form a metal oxidizing layer under applicable control of oxidizing voltage and time. Comparing with other prior arts, the process can proceed under room tempature without using expensive instruments and doesn't have a need to be produced under the high vacuum (<10 ⁻⁷ torr) environment. Therefore, both the thermal budget of the produced environment and producing cost could decrease effectually and easily being integrated to the present design condition and process installation.

[0043] 3. The invention uses liquid phase anodic oxidation under room tempature in the oxidation of the metallic layer, which can produce a ultrathin (EOT<20 Å) gate oxidizing layer with high quality and can be integrated to the present CMOS process directly without changing any process parameter and step to achieve minimizing devices as the final purpose.

[0044] 4. The liquid phase anodic oxidation used by the invention has a lot of choices and applications. For instance, to use one way such as evoparation, sputtering, MBE or CVD as a producing way. The metal for preparation can be a metal whose oxides are of high-k, such as aluminum (Al), tantalum (Ta), titanium (Ti), zirconium (Zr) or lanthanons (La). Anode is a chip and cathode can be a platinum (Pt) sheet or a N-semiconductor. Electrolyte can be DI water, other organic or inorganic electrolyte. Power supply for usage can be direct current (DC) anodic oxidation, alternating current (AC) anodic oxidation, direct-alternating current (DAC) anodic oxidation or constant current (CC) anodic oxidation. And thermal annealing installation can be furnace or rapid thermal annealing (RTA) installation. Thermal annealing gas can be nitrogen gas, oxygen gas, ammonia gas, nitrous oxide gas or forming gas (90% N₂+10% H₂). While using furnace, the annealing tempature is about between 500 to 900° C. and the annealing time is about 1 to 90 minutes. While using RTA installation, the annealing tempature is about between 800 to 1000° C. and the annealing time is about 0 to 60 seconds.

[0045] The following are advantages of the invention as above-mentioned,

[0046] (1) To decreases the thermal budget of the producing environment and producing cost effectually.

[0047] (2) To be integrated directly to CMOS process without changing any process parameter and step.

[0048] (3) Gate dielectrcs of high quality, high-k and ultrathin equivalent oxide thickness can be produced.

[0049] The present invention has been described with a preferred embodiment thereof and it is understood that many changes and modifications in the described embodiment can be carried out without departing from the scope and the spirit of the invention as defined by the appended claims. 

What is claimed is:
 1. A method of high-k gate dielectrics prepared by liquid phase anodic oxidation includes the following steps, to provide a silicon substrate and to produce a metallic film on the clean surface of a silicon substrate, then to oxidize the metallic film to form a metallic oxide as a gate oxidizing layer by liquid phase anodic oxidation, and to promote quality of said gate oxidizing layer by processing a step of thermal annealing.
 2. A method as claimed in claim 1, wherein anode is a silicon substrate, cathode is a platinum sheet or a N-semiconductor, electrolyte is DI water, other organic or inorganic electrolyte.
 3. A method as claimed in claim 1, wherein power supply for usage can be direct current anodic oxidation, alternating current anodic oxidation, direct-alternating current anodic oxidation or constant current anodic oxidation.
 4. A method as claimed in claim 1, wherein the metallic film produced on the surface of said silicon substrate must isolate to the electrode to make only the back of the silicon substrate to be contacted with the electrode so as to form a well-proportioned oxidizing electric field.
 5. A method as claimed in claim 1, wherein thermal annealing installation can be furnace or rapid thermal annealing installation.
 6. A method as claimed in claim 5, wherein thermal annealing gas can be nitrogen gas, oxygen gas, ammonia gas, nitrous oxide gas or forming gas (90% N₂+10% H₂).
 7. A method as claimed in claim 5, wherein the annealing tempature is about 500 to 900° C. while using furnace, and the annealing tempature is about 800 to 1000° C. while using rapid thermal annealing installation.
 8. A method as claimed in claim 5, wherein the annealing time is about 1 to 90 minutes while using furnace, and the annealing time is about 0 to 60 seconds while using rapid thermal annealing installation.
 9. A method as claimed in claim 1, wherein the producing way can be evaporation, sputtering, molecular beam epitaxy or chemical vapor deposition.
 10. A method as claimed in claim 1, wherein the metal for preparation can be a metal whose oxides are of high-k, such as aluminum, tantalum, titanium, zirconium or lanthanons.
 11. A method of producing a metal oxide semiconductor field effect transistor that contains high-k gate dielectrics includes the following steps, which first produces a p-well and a n-well on a silicon substrate and fills an oxide for isolation. Then to produce a metallic film on the surface of said clean silicon substrate and to oxidize said metallic film to form a metallic oxide as a gate-oxidizing layer by liquid phase anodic oxidation. Next to promote quality of said gate oxidizing layer by processing a step of thermal annealing to form a gate layer on the gate metal oxidizing layer. To definite gate region and to form the gate, drain and source of the transistor by ion implantation, then deposits an oxide-isolating layer on the gate layer. After etching the window of the gate, drain and source, to deposit a contact wire, and decreases concentration of junction traps by using thermal annealing.
 12. A method as claimed in claim 11, wherein anode is a silicon substrate, cathode is a platinum sheet or a N-semiconductor, electrolyte is DI water, other organic or inorganic electrolyte.
 13. A method as claimed in claim 11, wherein power supply for usage can be direct current anodic oxidation, alternating current anodic oxidation, direct-alternating current anodic oxidation or constant current anodic oxidation.
 14. A method as claimed in claim 11, wherein the metal film produced on the surface of said silicon substrate must isolate to the electrode to make only the back of the silicon substrate to be contacted with the electrode so as to form a well-proportioned oxidizing electric field.
 15. A method as claimed in claim 11, wherein thermal annealing installation can be furnace or rapid thermal annealing installation.
 16. A method as claimed in claim 15, wherein thermal annealing gas can be nitrogen gas, oxygen gas, ammonia gas, nitrous oxide gas or forming gas (90% N₂+10% H₂).
 17. A method as claimed in claim 15, wherein the annealing tempature is about 500 to 900° C. while using furnace, and the annealing tempature is about 800 to 1000° C. while using rapid thermal annealing installation.
 18. A method as claimed in claim 15, wherein the annealing time is about 1 to 90 minutes while using furnace, and the annealing time is about 0 to 60 seconds while using rapid thermal annealing installation.
 19. A method as claimed in claim 11, wherein the producing way can be evaporation, sputtering, molecular beam epitaxy or chemical vapor deposition.
 20. A method as claimed in claim 11, wherein a metal for preparation can be a metal whose oxides are of high-k, such as aluminum, tantalum, titanium, zirconium or lanthanons. 